Organic coating composition for an electrical steel sheet

ABSTRACT

An organic composition composed of the three main components, namely, the polyvinyl alcohol in an amount of 10 parts by weight, the styrene-type emulsion resin in an amount of 0.5 to 5 parts by weight and the water-soluble acrylic resin in an amount of 2 to 10 parts by weight. This composition is particularly effective as the coating for the electrical steel sheet, giving the excellent coating properties which could not be expected when each component were singly applied.

United States Patent [191 Kato et al.

[4 1 Dec.10,1974

[ ORGANIC COATING COMPOSITION FOR AN ELECTRICAL STEEL SHEET [75] Inventors: Hirotada Kato; Kazuo Nakamura;

Toshiya Wada, all of Kitakyushu,

Japan [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan [22] Filed: Feb. 5, 1974 [21] Appl. No.: 439,951

[30] Foreign Application Priority Data Feb. 12, 1973 Japan 48-17268 [52] US. Cl 260/901, 260/29.6, 260/42.52,

[51] Int. Cl. C08f 24/50 [58] Field of Search 260/901 [56] References Cited UNITED STATES PATENTS 2,773,050 12/1956 Caldwell et a1. 260/901 X Sirota 260/901 Russell 260/901 Primary Examiner-Murray Tillman Assistant Examiner-C. J. Seccuro Attorney, Agent, or FirmWatson Leavenworth Kelton & Taggart 5 7] ABSTRACT 5 Claims, No Drawings ORGANIC COATING COMPOSITION FOR AN ELECTRICAL STEEL SHEET BACKGROUND OF THE INVENTION It has heretofore been required that an iron core used for the transformer, generator, motor, etc. should have a high electric insulation resistance enough to protect the eddy current on its surface.

Also the iron core should be made of the electrical steel sheet having the good punchability since the core is manufactured by punching. The punchability of the electrical steel sheet may be affected by a lot of factors, one of which is the lubricating property of the surface of the electrical steel sheet. In connection with this, it is known that the punchability can be enhanced if the surface is coated with an organic substance.

The transformer, generator, motor, etc. in which the iron core is used will generate heat during the operation, whereby the temperature will be sometimes elevated up to about 150C. If, in this case, the organic coating has no heat resistivity, there is a danger of carbonization of the coated film and difficulty in operation of those apparatus.

It has heretofore been a practice to obtain an organic insulation coating by natural drying or low-temperature heat drying of organic resin which includes an organic solvent, whereby a time for drying is more or less required. In this case the coating solution is easily inflammable and thus full consideration should be paid to the construction of the drying unit.

It is therefore an object of the invention to provide a coating composition which is excellent in heat resistivity, which is available without any organic solvent and which makes possible the short-time curing or heating work at high temperatures that can not be carried out in the conventional coating treatment of the varnish system.

It is another object of the invention to provide a coating composition having other properties than the above, such as, electric insulation property, punchability, oil-proof property, corrosion-resistance and waterproof property, etc. which are equal to, or better than, those of the vamish-type coating composition of this kind.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a composition adapted for use in the electrical steel sheet which fomis an organic coating having good punchability, high electric insulation property, heat resistance and good adhesiveness.

In the prior art, it has been impossible to use the polyvinyl alcohol, or the styrene-type emulsion resin, or the water-soluble acrylic resin each singly for the purpose of coating the electrical steel sheet. In this invention, however, these three substances are mixed at a proper mixing ratio and used as the main components of the organic coating for the electrical steel sheet, whereby the properties required as such coating can successfully be obtained, Furthermore, as contrasted to the conventional C-3 oily varnish, it does notneed the organic solvent and makes possible the high-temperature, shorttime curing, the industrial value of which is quite high.

According to this invention, there is provided an organic coating composition adapted for use in the electrical steel sheet which comprises, as the main components, 10 parts by weight of the polyvinyl alcohol, 0.5 to 5 parts by weight, as the solid value, of the styrenetype emulsion resin and 2 to 10 parts by weight, as the solid value, of the water-soluble acrylic resin, said styrene-type emulsion resin containing at least 50% by weight of styrene. According to this invention, an electrical steel sheet having the above composition applied thereto is also provided.

The composition for forming the organic coating according to this invention is intended for coating the electrical steel sheet which is made of the silicon steel or the carbon steel. The percentage" or the part" used herein is based on the weight. This composition may be composed of a suspension of 0.5 to 5 parts, as the solid value, of the styrene-type emulsion resin containing at least 50% of styrene and 2 to 10 parts, as the solid value, of the water-soluble acrylic resin mixed in 10 parts of the polyvinyl alcohol, as the main components.

The polyvinyl alcohol used in this invention is one having the average polymerization degree between 500 and 2000 and the saponification degree between and 99 mol which may be partial saponification or complete saponification. If this polyvinyl alcohol only is dissolved in hot or cold water and applied to the electrical steel sheet, a uniform coating may be obtained. However, this coating is itself hygroscopic, poor waterproof property and thus can not be used practically. Moreover, it has poor heat resistivity. Accordingly, if the electrical steel sheet is subjected to the heat treatment at 200C X 48 hours, the coating is decreased in amount remarkably, turns its color and becomes brittle. Hereinafter it is referred to as having heatresistanee that the coating is not decreased so much in amount and does not change its color when subjected to the heat treatment.

The styrene-type emulsion resin used in this invention is the styrene emulsion resin, the styrene'acrylate emulsion resin, or the styrene-vinyl acetate emulsion resin, etc., which may be made from the styrene itself or from the copolymerization product of the styrene with the other monomer. In case of the copolymerization, the styrene should be contained in an amount of 50% or more. If the amount of the styrene is below 50%, the heat resistant property of the coating is so poor that when the styrene-type resin having not more than 50% styrene is singly applied to the electrical steel sheet, the loss of coating occurs after the heat treatment at 200C for 48 hours. Even when said resin is used in admixture with the polyvinyl alcohol and the water-soluble acrylic resin, the heat resistance of the coating is neverenhanced. However, in case of the styrene emulsion resin having at least 50% styrene, the heat resistance of the coating is remarkably improved. In case,'however, that the styrene-type emulsion resin having at least 50% styrene is singly applied to the electric steel sheet, the film can not be formed very well or the film can not be fomied uniformly. The adhesiveness of the coating is also poor. In addition, owing to the extreme thermoplasticity of the coating, the coating becomes softened during the applying or curing work, whereby the coating may be injured by rubbing with the hearth roll supporting the steel strip in the furnace. Also, its oil-proofness against the transformer oil, machine oil, etc. and its anti-solvent property against such organic solvent as acetone, xylene,-trichlene, are also so poor that the coating may easily be dissolved or swollen thereby. a

The water-soluble acrylic resin used in this invention may be the methyl acrylate resin, the ethyl acrylate resin, the butyl acrylate resin; the methyl methacrylate resin, the ethyl methacrylate resin, the butyl methacryl- 7 ate resin, or their copolymerized product.

It may also contain the acrylic resin which can be made water-soluble by dissolving into such alcohols as isopropyl alcohol, etc. having mutual solubility with water, even if it is not directly dissolved in water. When this water-soluble acrylic resin is singly coated and cured on the electrical steel sheet, the coating formed has poor heat resistivity as is the case with the polyvinyl alcohol, and poor adhesiveness.

As set forth above, when each of the polyvinyl alco* hol, the styrene-type emulsion resin and the watersoluble acrylic resin is singly applied to the electrical property of the polyvinyl alcohol can not be improved, while the styrene-type emulsion resin becomes too softened during curing to prohibit the occurring of scars thereon. On the other hand, if it is more than parts, the adhesiveness is insuificient and the heat resistivity is greatly deteriorated.

The main components of the organic coating composition for the electrical steel sheet according to this invention are the polyvinyl alcohol, the styrene-type emulsion resin, and the water-soluble acrylic resin. in addition thereto, a pigment or a resin equivalent to the pigment may be added. The amount of these substance to be added may vary with the degree of coloration desired, but the amount ranging between 0.2 and 2 parts based upon 10 parts of the polyvinyl alcohol is desirable. The resin equivalent orv corresponding to the pigment may be, for example, a sulfate of lignin for giving a brown color tone to the coating.

steel sheet as the coating composition, there are various defects occurring in the practical operation. After laboriously studying about these points, the inventors have found that when the polyvinyl alcohol, the styrene-type emulsion resin and the water-soluble acrylic resin are mixed at the ratio of 0.5 to 5 parts (as solid value) of the styrene-type emulsion resin and 2 to 10 parts (as solid value) of the water-soluble acrylic resin based on 10 parts of the polyvinyl alcohol to form a coating composition and the composition is coated on the electrical steel sheet, it shows the excellent coating properties required for the electrical steel sheet such as punchability, electric insulation property, high adhesiveness, heat resistivity, oil-proof and solvent-proof property, and so on. It is also found that a uniform coating having bright appearance can be formed by the high-temperature, short-time baking as distinguished from the low-temperature, long-time drying of the organic varnish.

By mixing the three components at the above-stated ratio, their merits, i.e., the uniform film-forming property, the high adhesiveness and the oil-proof property against transformer oil, etc. of the polyvinyl alcohol; the heat resistivity or the property of prohibiting the thermal softening of the styrene-type emulsion resin; and the solvent-proof property against various organic solvents of the water-soluble acrylic resin, etc. are effectively utilized, while their demerits, i.e., the poor corrosion-resistance, poor water-proof and poor heat resisting property of the polyvinyl alcohol; the poor film-forming and poor adhesive property of the styrene-type emulsion resin; and the poor heat resisting property of the water-soluble acrylic resin are supplemented and enhanced so as to make it possible to manufacture the coating having such properties as required as the organic coating for the electrical steel sheet.

The reasons for the limitation of the amount of the styrene-type emulsion resin and the water-soluble acrylic resin relative to l0 parts of the polyvinyl alcohol are as follows: Q

The styrene-type resin should be included in an amount of 0.5 to S'parts. If it is below 0.5 parts, the heat resistivity can not be improved appreciably. If it is more than 5 parts, the film-forming property is poor; the appearance has no brightness and the oiland solvent-proof property against the transformer oil and the organic solvent such as acetone, methanol, xylol is insufficient. As for the water-soluble acrylic resin, if it is below 2 parts, the corrosion-resistance and water-proof The conditions of curing the coating may be 40 seconds at the steel sheet temperature of 380C, or 15 seconds at 600C, which demonstrates that the hightemperature, short-time curing makes it possible to obtain a uniform coating.

Examples of the invention are indicated below.

Example I Polyvinyl alcohol (average polymerization degree 1000; saponification degree 88 mol 1 l0 parts Styreneacrylate emulsion (weight ratio:

styrene/butyl acrylate 8/2, as

solid value) 4 parts Water-soluble methacrylate resin (as I solid value) 2.5 parts Water parts Example 2 Polyvinyl alcohol (average pol merization) degree 500; saponification egree 88 mol l0 parts Wane emulsion (as solid value) 2 parts ater-soluble ethyl acrylate resin (as solid value) 4 parts Calcium lignin sulfonate (used instead of brown pigment) 1 1.5 parts Pigment (black) (Emacol Black C made by Sanyo Shikiso KK) 0.5 parts Water 50 parts Example 3 Pol nyl alcohol (average polymerization egree 2000, saponification degree 88 mol l0 parts Styrene-vinyl acetate emulsion (weight rtaio: styrene/vinyl acetate 6/4, as solid value) 1 part Water-soluble methyl acrylate resin (as solid value) 8 parts Pigment (brown) 0.5 arts Pigment (black) p (same as that used in Example 2 0.5 parts The treatment liquids of the above compositions .were coated uniformly on the electrical steel sheet in an amount of 4 to 6 g/m and heated at 380C for 30 seconds. The bright and uniform coatings were obtained. The properties such as the weight of coating, the inter-layer electric insulation resistance, the adhe- (Reference Example 2) of 40% (solid value) polystyrene, an aqueous solution (Reference Example 3) of 40% (solid value) acrylic resin were singly coated on the respective electrical steel sheets in an amount of 4 siveness, the corrosion resistance and water-proof 5 t0 6 g/m which were then Subjected to the heat treatproperty, the heat-resistivity, the oiland solvent-proof at for 30 Seconds- The Properties of the property, the punchability, etc. are indicated in Table Coatmgs obtalfled werefivaluated as Examples 1 t0 1 3. The result IS shown in Table l. The comparison of the test for heat resistivity between the commercially REFERENCE EXAMPLES 1() available 03 oily-type varnish (the weight of coating An aqueous solution (Reference Example 1) of 40% On the electrlcal steel sheet: 4 glm and the orgamc l i l l h l (average l i ti degree 500; composition described in Example 2 IS shown in Table saponitication degree 88 mol an emulsion solution Table 1 Properties Reference Reference Reference required for Example Example Example Example Example Example film l 2 3 l 2 3 Weight of coating (glm 5.4 4.2 4.0 4.l 4.3 4.3 Film-forming Good, Good, Good, Good, Bad. Slightly bad, property Luster Luster Luster Luster Lusterless Lusterless inter-layer resistance More than More than More than .Q-cm /sheet 500 500 l 500 250 500 I00 250 250 500 (by 118, 2nd test) m/m l0 m/mda l0 m/m l0 ml m m/mkb 3o m/mdz. Adhesiveness Bendin Bendin Bending, Bending, Bendin Bendin Not pee ed Not pee ed Not pee ed Not peeled Peele Peele Corrosion-resistance, waterroof property (5 C, No rust, No rust, No rust, Rust, Rust, Rust spots, in moisture Luster Luster Luster Lusterless Lusterless Lusterless vessel. 48 hrs.)

Heat resistivity, (After 200C X 48 hrs., weight 10.5 13.8 20.2 47.6 l2.3 43.2 loss Oil-proof property (Transformer No change No change No change No change Change No change No.2 Oil, 100C X 48 hrs.)

Solvent-proof property (Xylene, No change No change No change No change Change No change a C X 6 hrs.)

Table 2 Comparison of heat resistivity between the composition of Example 2 and the commercial oily-type varnish Heat Resistivit Composition *Loss after m [1W lC X 48 C X 30 after 200C hrs. days X 48 hrs.

Example 2 2.5 [0.2 l3.8 Commercial Varnish A 3.5 20.8 23.l

do. B 9.6 42.! 45.7 do. C ll.8 31.3 23.6

The decreased amount (/1) of the weight of the film.

The films obtained in the above Examples of this invention were all excellent in the inter-layer resistance, adhesiveness, heat-resistivity, corrosion-resistance and waterproof property, oil-proof property and solventproof property, and so on.

We claim:

1. An organic coating composition adapted for use in the electrical steel sheet which comprises, as the main components, (A) 10 parts by weight of polyvinyl alcohol,'(B) 0.5 to parts by weight, as the solid value, of styrene resin selected from the group consisting of styrene homopolymer and copolymers of styrene with vinyl acetate or alkyl acrylate and (C) 2 to parts by weight, as the solid value, of a watersoluble acrylic resin consisting essentially of at least one monomer selected from the group consisting of alkyl acrylate and alkyl methacrylate, said styrene resin containing at least 50% by weight of styrene.-

2. An organic coating composition according to claim 1 in which the polyvinyl alcohol is one having the average polymerization degree between 500 and 2000 3nd the saponification degree between 85 and 99 mol 3. An organic coating composition according to claim 1 in which the water-soluble acrylic resin is methyl acrylate resin, ethyl acrylate resin, butyl acrylate resin, methyl methacrylate resin, ethyl methacrylate resin, butyl methacrylate resin, or their copolymerized product.

4. An organic coating composition according to claim 1 which additionally contains a pigment.

5. An electrical steel sheet having an organic coating composition according to claim 1 applied thereto. 

1. AN ORGANIC COATING COMPOSITION ADAPTED FOR USE IN THE ELCTRICAL STEEL SHEET WHICH COMPRISES, AS THE MAIN COMPONENTS, (A) 10 PARTS BY WEIGHT OF POLYVINYL ALCOHOLS, (B) 0.5 TO 5 PARTS BY WEIGHT, AS THE SOLID VALUE; OF STYRENE RESIN SELECTED FROM THE GROUP CONSISTING OF STYRENE HOMOPOLYMER AND COPOLYMERS OF STYRENE WITH VINYL ACETATE OR ALKYL ACRYLATE AND (C) 2 TO 10 PARTS BY WEIGHT, AS THE SOLID VALUE, OF A WATERSOLUBLE ACRYLIC RESIN CONSISTING ESSENTIALLY OF AT LEAST ONE MONOMER SELECTED FROM THE GROUP CONSISTING OF ALKYL ACRYLATE AND ALKYL METHACRYLATE, SAID STYRENE RESIN CONTAINING AT LEAST 50% BY WEIGHT OF STYRENE.
 2. An organic coating composition according to claim 1 in which the polyvinyl alcohol is one having the average polymerization degree between 500 and 2000 and the saponification degree between 85 and 99 mol %.
 3. An organic coating composition according to claim 1 in which the water-soluble acrylic resin is methyl acrylate resin, ethyl acrylate resin, butyl acrylate resin, methyl methacrylate resin, ethyl methacrylate resin, butyl methacrylate resin, or their copolymerized product.
 4. An organic coating composition according to claim 1 which additionally contains a pigment.
 5. An electrical steel sheet having an organic coating composition according to claim 1 applied thereto. 